1. Field of the Invention
The present invention relates to an image blur prevention apparatus for preventing an image blur occurring in cameras, optical equipment, and so on.
2. Related Background Art
Video cameras or still cameras incorporating an image blur prevention apparatus are currently available, and such cameras are effective to take photographs with little fluctuation.
There are two types of image blur prevention apparatus mounted in such cameras, one of which is a type for effecting fluctuation correction by detecting fluctuation (vibration) of the camera from an image signal and correcting an electronic video signal, based thereon, and the other of which is a type for effecting fluctuation correction by mechanically and optically detecting fluctuation of the camera and mechanically and optically correcting the fluctuation. Each of these two types has both merits and drawbacks.
Explained below is a conventional example of a camera or a lens barrel as an optical device incorporating the image blur prevention apparatus based on the mechanical and optical principle.
The image blur prevention apparatus is comprised of, a well known, a fluctuation sensor for detecting an angular displacement, an angular acceleration, or an angular velocity of the optical device, a correcting means for correcting an image blur of the image plane, based on an output from the sensor, and a control means for controlling the fluctuation sensor and the correcting means.
FIG. 13 is a drawing for explaining a configuration of an image blur prevention apparatus using an angular velocity meter as a fluctuation sensor, which is a drawing to illustrate the principle of the image blur prevention apparatus for suppressing image blur due to vertical fluctuation 81p and lateral fluctuation 81y in the directions along arrows 81. In the drawing, reference numeral 82 designates a lens barrel of the camera, 83p an angular velocity meter for detecting an angular velocity of vertical fluctuation, 83y an angular velocity meter for detecting an angular velocity of lateral fluctuation, 84p a vertical detection output from the angular velocity meter 83p, 84y a lateral detection output from the angular velocity meter 83y, 85 a correction optical means, 86p and 86y drive coils of the correction optical means 85, and 87p and 87y position sensors for detecting vertical movement and lateral movement of the correction optical means 85.
In this image blur prevention apparatus, the image blur is corrected on the image plane 88 in such a manner that a control circuit (not shown) drives the correction optical means 85 by electric currents supplied to the drive coils 86p and 86y, based on the outputs 84p and 84y from the angular velocity meters 83p and 83y.
FIGS. 14A and 14B are structural drawings to show an example of a lens barrel having the correcting means formed based on the principle of image blur prevention as explained with FIG. 13, in which bearings 73y are pressed into a support frame 72 incorporating a lens 71 as a correction optical element, mounted by caulking. A support shaft 74y is supported on the bearings 73y so as to be slidable along the axial direction. A recess 74y a of the support shaft 74y is snap-fit with claws 75a of a support arm 75. Further, bearings 73p are also pressed into the support arm 75 so that a support shaft 74p can be supported as slidable along the axial direction.
FIG. 14B also includes a back side view of the support arm 75 at its lower right corner.
Light emitters 76p, 76y such as IREDs are bonded in emitter mount holes 72pa, 72ya in the support frame 72, and their terminals are soldered to lid 77p, 77y (bonded to the support frame 72) also serving as a connection board. Slits 72pb, 72yb are formed in the support frame 72 and light emitted from the light emitter 76p, 76y travels through the slit 72pb, 72yb to enter a PSD 78p, 78y as described below.
Coils 79p, 79y (corresponding to the coils 86p, 86y in FIG. 13) are also bonded to the support frame 72 and their terminals are soldered to the lid 77p, 77y.
Support balls 711 are fit (at three positions) in the lens barrel 710, and a recess 74pa of the support shaft 74p is snap-fit with claws 710a of the barrel 710.
Yokes 712p.sub.1, 712p.sub.2, 712p.sub.3, and magnets 713p are bonded in a stack, and similarly, yokes 712y.sub.1, 712y.sub.2, 712y.sub.3, and magnets 713.sub.y are also bonded in a stack. The polarities of the magnets are arranged as represented by the arrows 713pa, 713ya.
The yokes 712p.sub.2, 712y.sub.2 are screwed in associated recesses 710pb, 710yb of the barrel 710.
The position detectors 78p, 78y such as PSDs are bonded to sensor seats 714p, 714y (among which 714y is not shown) and the terminals of the position detectors 78p, 78y (corresponding to the sensors 87p, 87y in FIG. 13) are soldered to a flexible board (flexible printed-circuit board) 716, as being covered by sensor masks 715p, 715y. Dowels 714pa, 714ya (among which 714ya is not shown) of the sensor seats 714p, 714y are fit in mount holes 710pc, 710yc of the barrel 710 and the flexible board 716 is screwed to the barrel 710 using a flexible stay 717. Each ear 716pa, 716ya of the flexible board 716 is set through a hole 710pd, 710yd of the barrel 710 to be screwed onto the yoke 712p.sub.1, 712y.sub.1, and the coil terminals and emitter terminals on the lids 77p, 77y are connected to land portions 716pb, 716yb of the ears 716pa, 716ya of the flexible board 716 and to polyurethane copper wires (three-stranded wires).
A plunger 719 is screwed to a mechanical rocking chassis 718, and a mechanical rocking arm 721 charging a spring 720 is screwed to the mechanical rocking chassis 718 so that the plunger 719 can rotate about a fitting shaft screw 722.
The mechanical rocking chassis 718 is screwed to the barrel 710, and the terminals of the plunger 719 are soldered to lands 716b of the flexible board 716.
Adjusting screws 723 (at three positions) having spherical tips are screwed through the yoke 712p and the mechanical rocking chassis 718, so that sliding surfaces (hatched portions 72c) of the support frame 72 are sandwiched between the adjusting screws 723 and the support balls 711. The adjusting screws 723 are adjusted to be screwed as opposed to the sliding surfaces with a small clearance.
A cover 724 is bonded to the barrel 710 to cover the correction optical means 85 as described above.
FIG. 15 is a block diagram to show an example of a drive control circuit of the correction optical means, in which an output from the position detector 78p, 78y is amplified by an amplification circuit 727p, 727y and the thus amplified signal is input into the coil 79p, 79y to drive the support frame, thereby changing the output from the position detector 78p, 78y . When the drive directions (the polarities) of the coils 79p, 79y are set so as to decrease the outputs from the position detectors 78p, 78y (in negative feedback), the drive force of the coils 79p, 79y stabilizes the support frame 72 at a position where the outputs from the position detectors 78p, 78y become nearly zero.
Compensation circuits 728p, 728y are circuits for further stabilizing the control system, and driving circuits 729p, 729y are circuits for making up for currents applied to the coils 79p, 79y.
When command signals 730p, 730y are supplied from the outside to the system of FIG. 15, the support frame is driven so as to be very faithful to the command signals 730p, 730y.
The technique for controlling the coils by negatively feeding the position detection outputs back as in the control system of FIG. 15 is called as a position control technique, in which, when an amount of hand fluctuation is given as a command signal 730p, 730y, the support frame 72 is driven in proportion with the amount of hand fluctuation.
FIG. 16 is a detailed diagram to show a specific example of the drive control circuit of FIG. 15 for driving the correction optical means, which shows a drive control means in the pitch direction. (The drive control means for the yaw direction has the same structure.)
In FIG. 16, current-voltage conversion amplifiers 732pa and 732pb convert photocurrents 731pa and 731pb occurring on the position detector 78p receiving light from the light emitter 76p into voltages, and a differential amplifier 733p earns a difference between the current-voltage conversion amplifiers 731pa and 731pb (an output proportional to the position in the pitch direction 725p of the support frame 72). These current-voltage conversion amplifiers 732pa, 732pb and differential amplifier 733p correspond to the amplification circuit 727p of FIG. 15.
A command amplifier 734p adds a command signal 730p to an output from the differential amplifier 733p and outputs the result to a drive amplifier 735p. The drive circuit 729p is composed of the drive amplifier 735p, transistors 736pa, 736pb, and a resistor 737p.
Resistors 738p, 739p and a capacitor 740p compose a well known phase lead circuit, which corresponds to the compensation circuit 728p.
A summing amplifier 741p receives a sum of outputs from the current-voltage conversion amplifiers 732pa , 732pb (a sum of receiving light quantities of the position detector 78p) and supplies it to an emitter drive amplifier 742p.
The light emitter 76p changes its emitting light quantity on a very unstable basis depending upon the temperature or the like, and the sensitivity of position detection of the differential amplifier 733p changes depending thereon. However, the change in the sensitivity of position detection becomes smaller when the light emitter is driven by the sum of receiving light quantities of the position detector 78 as described above (or by the constant receiving quantity control for increasing the emitting light quantity of the light emitter 76p as the sum of receiving light quantities becomes smaller).
An engagement means 61 for engagement of the support frame 72 is next explained referring to FIGS. 17A, 17B, 17C and FIGS. 14A and 14B.
The engagement means 61 is composed of the mechanical rocking chassis 718, plunger 719, spring 720, mechanical rocking arm 721, and shaft screw 722 as explained with FIGS. 14A and 14B. FIGS. 17A and 17B show views of the engagement means 61 when observed along the directions of arrows 718a, 718b in FIG. 14A, and FIG. 17C shows a cross section of the plunger 719.
In FIG. 17C the plunger 719 is composed of a slider 719a, a stator 719b, and, a coil 719c and a permanent magnet 719d mounted in the stator 719b. As shown in FIG. 17A, the slider 71a is hooked on a hole 721b of the mechanical rocking arm 721 rotatably supported by the shaft screw 722, and the mechanical rocking arm 721 is rotationally energized in the direction of arrow 720a by the spring 720. Because of this arrangement, the slider 719a is always subject to such drawing force F.sub.OUT as to draw it out of the stator 719b. However, because the slider 719a is in contact with the permanent magnet 719d, the attractive force is so great as not to move the slider by the force of spring 720 (F.sub.mg &gt;F.sub.OUT where F.sub.mg is the attractive force of the permanent magnet).
In this state a dowel 721a at the tip of the mechanical rocking arm 721 is fit in a hole 72d of the support frame 72, thereby stopping the support frame 72.
When an electric current then flows in a desired direction in the coil 719c, it changes a flow of magnetic flux of a magnetic circuit comprised of the permanent magnet 719d, the slider 719a, and the stator 719b, thereby weakening the attractive force between the slider 719a and the permanent magnet 719d. Then the force of spring 720 rotates the mechanical rocking arm 721 in the direction of arrow 720a, whereby the dowel 721a leaves the hole 72d, thereby releasing the engagement (F.sub.OUT &gt;F.sub.mg -F.sub.i where F.sub.i is the repulsive force due to the current).
The slider 719a is also drawn out of the stator 719b on this occasion, and a gap .delta. appears between the slider 719a and the permanent magnet 719d.
Since the attractive force is inversely proportional to the square of the distance between the permanent magnet and an opposed object, as is well known, the attractive force becomes extremely smaller because of occurrence of the gap .delta..
After the supply of current to the coil 719c is interrupted, the disengaged state of the support frame 72 is maintained by the urging force of the spring 720.
When the electric current is next supplied in the opposite direction to the coil 719c, a resultant force of the attractive force of the slider 719a by this current and the attractive force of the permanent magnet 719d becomes greater than the force of the spring 720 so as to draw the slider 719a into the stator 719b (F.sub.mg +F.sub.i &gt;F.sub.OUT).
Once the slider 719a starts being drawn into the stator 719b, a decrease in the gap .delta. accelerates to increase the attractive force of the permanent magnet, so that the slider 719a comes to contact the permanent magnet 719d whereby the dowel 721a comes to fit in the hole 72d again to engage with the support frame 72.
As explained above, a bistable structure is realized for holding each state by supplying the electric current to the plunger only upon engagement or upon engagement release, thereby achieving a compact and power-saving engagement means.
FIGS. 18A and 18B are block diagrams to show the scheme of the control system of a camera equipped with the conventional image blur prevention apparatus as described above, in which reference numeral 91 denotes a fluctuation detection means corresponding to the angular velocity meter 83p, 83y in FIG. 13, which is composed of a fluctuation detection sensor for detecting the angular velocity, such as a vibration gyro, and a sensor output calculation means for cutting dc components in an output from the fluctuation detection sensor and thereafter integrating the output to obtain an angular displacement.
An angular displacement signal from the fluctuation detection means 91 is input into a target value setting means 92. The target value setting means 92 is composed of a variable differential amplifier 92a and a sample-and-hold circuit (S/H) 92b, and two signals input to the variable differential amplifier are always equal because the sample-and-hold circuit 92b is always in sampling. Thus, the output from the sample-and-hold circuit 92b is zero. However, once the sample-and-hold circuit 92b switches to a hold state due to an output from a delay means 93 as described below, the variable differential amplifier starts continuously supplying outputs from zero of that time.
An amplification factor of the variable differential amplifier 92a is arranged as variable by an output from a means 94 for setting the sensitivity of image blur prevention (sensitivity setting means). The reason for the variable arrangement is as follows. A target value signal of the target value setting means 92 is a target value (command signal) for the correction means 910 to follow up. A correction amount of the image plane to a drive amount of the correction means (the sensitivity of image blur prevention) changes depending upon optical characteristics based on a focus change in zooming or in focusing. Therefore, the amplification factor is changed to compensate for the change in the sensitivity of image blur prevention. The sensitivity setting means 94 is thus arranged to receive focal length information upon zooming from a zoom information output means 95 and focal length information upon focusing based on distance measurement information of an exposure ready means 96, and to calculate the sensitivity of image blur prevention based on the information or to extract information on the sensitivity of image blur prevention preliminarily set based on the information, thereby changing the amplification factor of the variable differential amplifier 92a in the target value setting means 92.
The correction means 910 shown in FIG. 18B is one in the sense of the wide concept also including those other than the above correction optical means 85.
A correction drive means 97 is the control circuit shown in FIG. 15, to which the target value from the target value setting means 92 is input as a command signal 730p, 730y.
A correction start means 98 is a switch for controlling connection between the drive circuit 729p, 729y and the coil 79p, 79y in FIG. 15, in which a switch 98a is connected to a terminal 98c in a normal condition to short-circuit the both ends of each coil 79p, 79y and in which, when a signal from a logical product means 99 is input, the switch 98a is connected to a terminal 98b to turn the correction means 910 into a control state (in which fluctuation correction is not carried out yet, but the power is supplied to the coil 79p, 79y to stabilize the correction means at the position where the signal from the position detector 78p, 78y is nearly zero). Further, the signal from the logical product means 99 is also supplied to the engagement means 914 on this occasion, whereby the engagement means 914 releases the engagement with the correction means 910.
The correction means 910 supplies the position signal from the position detector 78p, 78y to the correction drive means 97 to effect the position control as described above.
The logical product means 99 is arranged so that an AND gate 99a supplies an output when it receives both an on signal of switch SW1 operating in synchronization with half depression of a shutter release button of a release means 911 and a signal from an image blur prevention switch means 912. Namely, when a photographer actuates the image blur prevention switch of the image blur prevention switch means 912 and when the switch SW1 as the release means is turned on, the correction means is released from engagement into a control state.
The on signal of SW1 from the release means 911 is also supplied to the exposure ready means 96, which performs photometry, distance measurement, and lens in-focus driving and which outputs the focal length information upon focusing to the sensitivity setting means 94 as discussed above.
The delay means 93 receives the signal from the logical product means 99 and outputs it, for example, one second later, thereby making the target value setting means 92 output the target value signal, as described above.
The on signal of SW1 from the release means 911 is also input to the fluctuation detection means 91 to start the fluctuation detection means. As described previously, the sensor output calculation means including a large-time-constant circuit such as an integrator needs a certain time between start and stabilization of output.
The delay means 93 plays a role of outputting the target value signal to the correction means after waiting before the output from the fluctuation detection means becomes stabilized, and starts image blur prevention after the output from the fluctuation detection means becomes stabilized.
Receiving an on signal of switch SW2 operating in synchronization with full depression of the shutter release button of the release means 911, the exposure means 913 moves a mirror up, opens and closes the shutter at the shutter speed obtained based on the photometric value of the exposure ready means 96 to effect exposure, and then moves the mirror down to complete photographing.
When after photographing the photographer frees the release button of the release means 911 to turn SW1 off, the logical product means 99 stops its output to change the sample-and-hold circuit 92b of the target value setting means 92 into a sampling state, thereby changing the output from the variable differential amplifier 92a to zero.
Thus, the correction means 910 returns to the control state in which the correction drive is stopped.
When the output from the logical product means 99 becomes off, the engagement means 914 engages with the correction means 910, and thereafter the switch 98a of the correction start means 98 is connected to the terminal 98c so as to bring the correction means 910 out of the control state.
The camera with the conventional image blur prevention apparatus as described above had the following problems to be solved.
As explained with FIGS. 18A and 18B, the operation of the image blur prevention apparatus is effected in such a manner that the image blur prevention switch means 912 as a main switch of image blur prevention is turned on to supply the power to the circuits in the image blur prevention apparatus, the fluctuation detection means is started by half depression of the shutter release button of the release means 911 (by the on signal of SW1), and then image blur prevention is started after the time delay of t.sub.1.
Some types of recent cameras have a real time m(de (which is a mode of short release time lag in which exposure is started within a very short time after the switch SW2 synchronized with full depression of the release button is turned on), and such types of cameras are often demanded to have a rapid photographing property.
Even among a cameras not having the real time mode, some models are particularly preferred by users desiring a rapid photographing property for the reasons including the relatively small release time lag, the quick shutter speed, etc.
There appear the following problems as inconveniences in use when the lens barrel with the conventional image blur prevention apparatus is mounted on such a camera.
(1) It is necessary to start exposure after the image blur prevention apparatus becomes accurately effective with a lapse of the time t.sub.1 in the half-depression state of the release button (while SW1 is kept on), which causes the problem that the waiting time t.sub.1 is troublesome when rapid photographing is preferred. If exposure were started without a lapse of time t.sub.1, image degradation due to hand fluctuation would not be avoided. PA1 (2) Generally, rapid photographing is necessary in sports photographing or the like, and frequent framing changes are necessary in such cases. When the image blur prevention is effective in that case, the image blur prevention apparatus also corrects even the framing changes, resulting in the problem that the framing changes are not allowed. PA1 (3) A switch for controlling the image blur prevention apparatus is mounted on the lens barrel including the correction optical means. When the control switch for image blur prevention is mounted on the lens barrel side in this manner, the switch could be often left on, which could cause the following problem. Namely, supposing the lens barrel with the image blur prevention function is taken away from the camera after photographing with the control switch for image blur prevention left on, then a lens barrel without the image blur prevention apparatus is mounted on the camera to continuously take some photographs, and thereafter the lens barrel with the image blur prevention function is again mounted on the same camera. Image blur prevention is started even though the photographer does not intend to effect image blur prevention. This has resulted in the problem that a framing change is not possible. PA1 (4) In the prior-art case as described above, the time constant of the sensor output calculation circuit is changed in order to quickly stabilize the fluctuation correction target output, immediately after start of the fluctuation detection means. This change of the time constant is a known technique. When an extremely small time constant is changed into a large time constant convenient for image blur prevention in order to quickly stabilize the fluctuation correction target output (when a change amount of the time constant is set greater), it can quickly remove low-frequency errors (hereinafter referred to as bias errors) close to the dc bias components overlaid on the fluctuation detection means, but components close to frequencies of hand fluctuation can rarely be removed. Thus, for example when image blur prevention with high accuracy is carried out as in long-time exposure, a certain waiting time is necessary before this error (hereinafter referred to as a phase error) stops.
Generally, a photographer frequently repeats half depression of the shutter release button (this operation also effects focusing and photometry in the case of an automatic focusing camera) as aiming the camera at an object, though it is also the case with normal cameras (those not needing the rapid photographing property). This is for correcting deviations of focus and photometry value due to the framing change. However, this has resulted in the problem that the photographer must wait a time t.sub.1 every framing change with the camera having the above image blur prevention apparatus, which is burdensome.
Especially, if the above control switch for image blur prevention also serves as an engagement interlocking mechanism of the correction optical means and when the lens barrel is taken off from the camera as leaving the switch on, the correction optical means is kept in a disengaged state, and thus, the correction optical means fluctuates while the photographer carries the lens barrel. This would result in unfavorable touching or damaging of the lens barrel. When the lens barrel is again mounted on the camera body to start photographing, the correction optical means is not controlled at all and is in the disengaged state before half depression of the release button. Then the correction center of the correction optical means would not be coincident with the optical-axis center of the lens in many cases. In such cases, when the correction optical means came to be controlled by half depression of the release button so as to make the image blur prevention effective, there occurred the problem that framing was deviated from that before start of image blur prevention.
On the contrary, when a certain time constant not so small was changed into a large time constant (when a change amount of the time constant was set smaller), there was the problem that a certain time was necessary for removing the bias errors while the phase error described above was able to be quickly removed.